The hydrogen evolution/oxidation reactions (HER/HOR) play an important role in hydrogen energy conversion devices. Nevertheless, the poor understanding of the sluggish HER/HOR kinetics on Pt in alkaline media is still a bottleneck. Herein, we have prepared a series of Pt–rare earth (RE) nanoalloys and, for the first time, systematically evaluated them towards the alkaline HER/HOR, and have identified the effect of the lanthanide contraction. Operando XAS measurements revealed that the induced compressive strain is not the sole kinetic descriptor, and that the chemical nature of the RE might modulate the adsorption and mobility of oxygenated-species, boosting the electrochemical reactions kinetics. This work provides insights on the property–activity trends of the unexplored Pt–RE/C nanoalloys in alkaline solution, and might inspire the rational design of electrocatalysts for the alkaline HER/HOR.